8262049: [TESTBUG] Fix TestReferenceRefersTo.java for Shenandoah IU mode

Reviewed-by: kbarrett, zgu

test/hotspot/jtreg/gc/TestReferenceRefersTo.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2021 Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -197,8 +197,6 @@ public class TestReferenceRefersTo {
             expectCleared(testPhantom1, "testPhantom1");
             expectCleared(testWeak2, "testWeak2");
             expectValue(testWeak3, testObject3, "testWeak3");
-            // This is true for all currently supported concurrent collectors.
-            expectNotCleared(testWeak4, "testWeak4");
 
             progress("verify get returns expected values");
             if (testWeak2.get() != null) {
@@ -213,11 +211,6 @@ public class TestReferenceRefersTo {
             }
 
             TestObject obj4 = testWeak4.get();
-            if (obj4 == null) {
-                fail("testWeak4.get() returned null");
-            } else if (obj4.value != 4) {
-                fail("testWeak4.get().value is " + obj4.value);
-            }
 
             progress("verify queue entries");
             long timeout = 60000; // 1 minute of milliseconds.
@@ -243,10 +236,10 @@ public class TestReferenceRefersTo {
                 fail("testWeak2 not notified");
             } else if (testWeak3 == null) {
                 fail("testWeak3 notified");
-            } else if (testWeak4 == null) {
-                if (obj4 != null) {
-                    fail("testWeak4 notified");
-                }
+            }
+            if ((testWeak4 == null) != (obj4 == null)) {
+                fail("either referent is cleared and we got notified, or neither of this happened: referent: "
+                     + obj4 + ", notified: " + (testWeak4 == null));
             }
 
         } finally {

test/hotspot/jtreg/gc/TestReferenceRefersToDuringConcMark.java

@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2020, 2021 Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package gc;
+
+/* @test
+ * @requires vm.gc != "Shenandoah" | vm.opt.ShenandoahGCMode != "iu"
+ * @library /test/lib
+ * @build sun.hotspot.WhiteBox
+ * @modules java.base
+ * @run main ClassFileInstaller sun.hotspot.WhiteBox
+ * @run main/othervm
+ *      -Xbootclasspath/a:.
+ *      -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
+ *      gc.TestReferenceRefersToDuringConcMark
+ */
+
+import java.lang.ref.Reference;
+import java.lang.ref.WeakReference;
+import sun.hotspot.WhiteBox;
+
+public class TestReferenceRefersToDuringConcMark {
+    private static final WhiteBox WB = WhiteBox.getWhiteBox();
+
+    private static volatile Object testObject = null;
+
+    private static WeakReference<Object> testWeak = null;
+
+    private static void setup() {
+        testObject = new Object();
+        testWeak = new WeakReference<Object>(testObject);
+    }
+
+    private static void gcUntilOld(Object o) throws Exception {
+        if (!WB.isObjectInOldGen(o)) {
+            WB.fullGC();
+            if (!WB.isObjectInOldGen(o)) {
+                fail("object not promoted by full gc");
+            }
+        }
+    }
+
+    private static void gcUntilOld() throws Exception {
+        gcUntilOld(testObject);
+        gcUntilOld(testWeak);
+    }
+
+    private static void fail(String msg) throws Exception {
+        throw new RuntimeException(msg);
+    }
+
+    private static void expectNotCleared(Reference<Object> ref,
+                                         String which) throws Exception {
+        if (ref.refersTo(null)) {
+            fail("expected " + which + " to not be cleared");
+        }
+    }
+
+    private static void expectValue(Reference<Object> ref,
+                                    Object value,
+                                    String which) throws Exception {
+        expectNotCleared(ref, which);
+        if (!ref.refersTo(value)) {
+            fail(which + " doesn't refer to expected value");
+        }
+    }
+
+    private static void checkInitialStates() throws Exception {
+        expectValue(testWeak, testObject, "testWeak");
+    }
+
+    private static void discardStrongReferences() {
+        testObject = null;
+    }
+
+    private static void testConcurrentCollection() throws Exception {
+        setup();
+        gcUntilOld();
+
+        WB.concurrentGCAcquireControl();
+        try {
+            checkInitialStates();
+
+            discardStrongReferences();
+
+            WB.concurrentGCRunTo(WB.BEFORE_MARKING_COMPLETED);
+
+            // For most collectors - the configurations tested here -,
+            // calling get() will keep testObject alive.
+            if (testWeak.get() == null) {
+                fail("testWeak unexpectedly == null");
+            }
+
+            WB.concurrentGCRunToIdle();
+
+            expectNotCleared(testWeak, "testWeak");
+        } finally {
+            WB.concurrentGCReleaseControl();
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        if (WB.supportsConcurrentGCBreakpoints()) {
+            testConcurrentCollection();
+        }
+    }
+}